1970 年 23 巻 1 号 p. 32-40
On February 21, 1968, a large earthquake occurred at Ebino plateau, south-west part of Miyazaki Pref. in Kyushu. Since then, Ebino earthquake swarm had been active for about one year. Abuyama Seis. Obs., Sakurajima Volcano. Obs. and Disast. Prey. Res. Inst. of Kyoto Univ. made the temporary observation at 5 stations. The main results on the nature of the Ebino earthquake swarm are as follows:
1) The epicentral region characteristically changed its shape with time.
2) The aspects of the push-pull distribution of the initial P motions appeared to be nearly the same both in large shocks and microearthquakes, showing the same focal mechanism in both cases. This phenomenon does not seem to vary throughout the whole period of this study.
3) According to the wave-period analysis, we recognized the interesting relation between the location of the epicenter and the _frequency of those shocks. It may be considered that this was caused by the difference of the properties of the crustal rocks in the hypocentral region from those outside the focal area.